Back when I was more of an idiot writer, I'd do this thing where I'd finish a draft and immediately start trying to "fix" it. What I would usually end up with afterwards was another first draft. Somehow in my efforts to make the story better, I ended up making it different and more complicated than I ever planned to. After years of doing this, I figured out some tips to help me. Here they are.

1.) Stop adding on!
Imagine that your story is the earth. You have land and sea. Don't try to add more land. Leave it alone. Have some confidence in the story that you wrote and trust it.

2.) Solve your world's problems!
Make sure that your story stays true to itself. If you establish a key plot point, don't change it halfway through. Are your characters consistent? Do you break your own rules just to make the plot easier? Then don't. Find them and fix them.

3.) Fix your grammar!
Seriously. Spell check--twice if you must. Nothing ruins a story faster that grammatical errors and fragmented sentences.

4.) Ask someone to read it to you!
It helps. If you cringe at the sound of your words coming out of someone else's mouth, you might want to think about making a few changes.

5.) It's ok to change goofy dialogue!
Sometimes we write things and they just sound stupid. Especially if you have a character that just curses all the time. Find something else for them to say. Be creative. Have fun. Your story will thrive because of it.

Above all, remember that rewrites aren't about doing more, they're about doing less. The bulk of your work had already been done in the first draft.